1. Field of the Invention
The present invention generally relates to a process for removal of noble metal-based materials, and more particularly in a preferred aspect to “dry” etching of deposited iridium-based materials to fabricate microelectronic device structures.
2. Description of the Related Art
Iridium (Ir) and iridium oxide (IrO2) are of great interest for use as electrode materials in both dynamic random access memories (DRAMs) and for ferroelectric-based memory devices (e.g., FRAMs) that incorporate perovskite metal oxide thin-films as the capacitor layer.
The advantages of Ir over other possible electrode materials include ease of deposition, e.g., using chemical vapor deposition (CVD), the ability to “dry” etch the material, the ability to form a stable conducting oxide (IrO2) at high temperatures in an oxidizing environment, the ability to convert IrO2 back to Ir metal at suitable temperatures (on the order of 350° C.) in forming gas, and the ability of the corresponding product microelectronic device to operate stably at high temperatures with a high degree of reliability.
The deposition and/or processing of Ir-based electrodes is highly desirable based on the above-discussed advantages. Ir displays a resistivity 5.3 μΩ-cm at 20°C. and IrO2 is highly conducting with a reported resistivity of 100 μΩ-cm. The formation of IrO2 occurs only at elevated temperatures (>550°C.) in O2 and is a superior material for the deposition of complex oxides for dielectric or ferroelectric capacitors. Further, during the high temperature CVD process for the growth of these capacitors, the formation of IrO2 can be advantageous for limiting inter-diffusion, as for example by acting as a diffusion barrier to oxidation of conducting polysilicon vias or plugs. IrO2 therefore is a material having many advantages in forming a robust, low-leakage electrode for reliable device fabrication.
Based on the need for Ir-based electrodes, a facile etching method for Ir is critical for commercial manufacturing processes, particularly those involving CVD techniques, since CVD enables the fabrication of electrode structures having dimensional characteristics below 0.5 micron.
In order to obtain useful electrode structures, it generally is necessary to etch the deposited Ir-based material, to form elements of a desired dimensional and locational character. Heretofore, “dry” etching techniques utilizing plasma for reactive ion etching (RIE) have been generally chlorine-based and resulted in significant residue being left on the structure after completion of the etching process.
Depending on the type of structure being formed, such post-etch residue can result in short circuiting, undesirable topography and/or other deficiencies in the subsequent operation of the product microelectronic device. Prevention of the formation of such residues can be achieved in some instances by manipulating the reactive ion etching (RIE) process parameters, but such process manipulation produces undesirable sidewall slopes in the microelectronic device structure that in turn prevent useful submicron capacitors from being fabricated from iridium-based materials.
Accordingly, it would be a significant advance in the art of fabricating microelectronic devices and precursor structures therefor, to provide a simple and commercially useful “dry” etch methodology applicable to Ir-based materials that provides high etching rates, superior etching uniformity and effective control over the shape of the etched features.